rendercheck is a program to test a Render extension implementation against
separate calculations of expected output.

Tests currently include:
- Destination coordinates correctness
- Source coordinates correctness
- Transformed (FilterNearest) source coordinates correctness.
- Composite with and without mask (with/without component alpha), with 1x1
  repeating Pictures and 10x10 Pictures.
- Linear gradients
- Repeating sources/masks at POT and non-POT sizes
- Some regression tests for bugs from freedesktop.org bugzilla.

rendercheck uses the Meson build system, which uses the "ninja" build
backend on Linux.  The three commands to configure (building into the
build/ directory), build, and install are:

    meson build/
    ninja -C build/
    sudo ninja -C build/ install